A plethora of carcass grading systems and techniques have been developed which attempt to relate carcass characteristics to yield; most are performed manually and are therefore inherently subject to variations. With the intention of eliminating operator variability, I have previously devised an automatic inspection system using video cameras and image analysis; the system is disclosed in GB2247524 which is incorporated herein by reference. The system provides information on specific sex, distribution and other attributes through examination of the total carcass so as to determine an overall grade: weighting factors, such as carcass weight and size, may be applied if thought desirable. Normalised measurements are used to predict meat yield by reference to data from prior measurement of reference carcasses; as the database on which prediction of meat yield expands, the precision and accuracy of prediction steadily improves. Examination of the carcass can provide at best only a crude estimate of the quality of the meat itself.
One of the main causes of variability in the quality of meat and meat products is the variability of the meat cuts from which the meat is derived or which provide the raw material for the process concerned. Many of the causes of this variability have been identified, at least in broad sweep, but in practical terms the control of the causes that lead to such variability is extremely difficult. This is particularly the case from the point of view of the producer of meat animals, who is frequently faced with a highly variable and poorly defined genotypic pool, on which has to be superimposed a wide variety of environmental factors which contribute to the rate that the animal grows and the deposition of the relative proportions of the various tissues that make up the animal at slaughter. Further, the complex interplay between genotype and environment is only partly understood and inadequately defined. Consequently, both the fresh meat handler and the manufacturer of meat products are likely to be faced with the problem of unpredictably variable raw material for the foreseeable future.
In some respects, the great diversity of meat products that are available in the market today has originated in response to the variability in raw material characteristics, with particular types of cut tending to be used for product manufacture (because their appearance is not aesthetically attractive visually, for example, or their high content of connective tissue makes them unacceptably tough, etc) and the need to maximise return from individual cuts that are not of sufficient quality to be sold without processing. Despite the long history of meat processing, it is still common practice for manufacturers of meat products to select meat cuts according to criteria largely based on experience on one hand, and customers' requirements on the other. Where, as in many cases, this selection is largely manual and frequently subjective, it is typically somewhat slow, requires skill and experience on the part of the selector, and in practice is found to provide an unacceptably high incidence of unsatisfactory product. Where the selection is made on more objective criteria, such as weight, it may be less error prone; however, variability in the finished product is still too high, probably because the relationship between the objective value measured and the quality criterion in the end product is poor. These problems are further complicated and exaggerated in the large-scale manufacture of meat products, where throughput has to be high enough to handle the meat from several thousand animals a day, and allocate the individual cuts of meat to a particular product line at the same time. The vagaries of supply of raw material, and the need to be able to respond rapidly to a change in customers' requirements, places an increasing requirement for flexibility in manufacture.
The situation is a general and familiar one relating to all cuts of meats from all meat species, and is well exemplified in the processing of pig legs to hams. At one extreme of the spectrum of products that may be manufactured from a pork leg is the traditional ham, which is often sold as an intact, bone-in joint which may have taken weeks or even months between the time of excision from the pig carcass to the sale and consumption of the end product. At the other end of the spectrum, there are the products of the latter-day technologies such as tumbling and massaging, in which boneless pieces of meat are mechanically agitated and recombined during cooking; these products may be ready for sale within a few days of excision. The price per unit mass of the finished product commanded by the traditional ham is frequently considerably greater than that of the modern ham.
A quality parameter that is considered essential in most meat processing plants is the weight of end product sold related to the weight of raw material used in the process concerned. In the manufacture of hams from uncured pork legs, this weight is usually expressed as a yield, defined as the weight of end product expressed as a percentage of the weight of the pork leg. It is important that the yield is predictable within as closely defined limits as possible, in order to meet customers' specifications, and frequently also legislation. For this reason, yield is always a major criterion in any meat manufacturing plant, and it is often the only quality criterion used regularly in small meat processing plants. Similar considerations apply in connection with the meat carcass from which the cuts have originated.
The accurate prediction of weight of end product obtainable from an individual cut of meat is an ideal which has been sought throughout the meat industry for decades. The fatness of a meat cut may be a factor contributing to the variability in yield of cuts of meat, but the relationship is not well defined.
The term "fatness" relates not just to the total amount of fat in a cut, but also its distribution. A cause of complaint in the manufacture of traditional, bone-in ham is attributable to the variability in the magnitude of appearance of popliteal fat, which appears between blocks of muscle at the distal part of the leg behind the knee joint. The appearance of this fat depot has lead to its common name "star" fat. Excessive star fat is only seen in a traditional ham when it is sliced at the point of sale. Since conventional methods of quality control have failed to predict the predisposition of individual pigs to exhibit objectionable amounts of star fat, the complaint occurs at the point of sale to the domestic customer. Such complaints cause dissatisfaction (and incur expense) at all links in the chain between the product manufacturer and the consumer.
The occurrence of excessive star fat is not only unsightly, it also causes problems in the slicing of hams off the bone. Slices of ham containing large amounts of star fat between the muscle blocks tend to fall apart during and after slicing, leading to an unacceptably high incidence of rejected slices. If it were possible to identify before manufacture those pork legs most likely to exhibit unsatisfactory amounts of star fat, then these legs could, for example, be re-routed for the manufacture of lower value, boneless hams, when the popliteal fat could be removed by butchery.
Pig loins are less well-suited to tumbling or massaging, but the removal of subcutaneous fat from around the eye muscle is inherently simpler manually. The amount of fat trimmed may vary, for example removing as much of the fat as possible to leave a high-lean cut, or trimming less severely to provide a loin in which the eye muscle has an even fat thickness along its entire length. The resultant cut may be bone-in or boneless. Trimming of this sort may be undertaken as a routine matter (for example where the larger cross-sectional area of a more mature animal is considered advantageous but the associated fat is considered detrimental) or in cases where the amount of fat present over the eye muscle varies from animal to animal, in which case the trimming is intended to bring individual cuts within specification. In either case, the fat removed will typically be used for further manufacture, usually for comminuted meat products. Loins may be trimmed in this fashion to provide otherwise unprocessed cuts of high lean content, or the trimmed lean may be cured, smoked, etc.
Although trimming loins is inherently simple, it is also inherently slow when done manually (at least to achieve a high degree of evenness of trim without damaging the eye muscle), especially since a barrier to the increase in speed that may be achieved manually is an associated increase in risk of injury to the operatives. Loin pulling machines are available which attempt to overcome these difficulties. In essence, these consist of U-shaped flexible knives the design of which has evolved from similar implements used manually. Although mechanised, such apparatus still requires human control and supervision. In practice, the quality of trim achievable with these machines is not high, and in many cutting plants a secondary trimming is often performed manually.
The colour of meat and products is important. Products or cuts that are paler or darker than the normal expected for a particular cut or type of product are usually less desirable to the consumer.
Another cause of complaint is variability in colour. Where such variability is present in a pig leg, the leg can in principle be routed for boneless ham manufacture where, for example, muscles from a large number of pig legs may be selected on the basis of colour such that variability in colour in the end product is reduced to a minimum. Selection "by eye" is, of course, applicable in this situation, but it is found to be surprisingly unreliable, perhaps due to poor and variable lighting conditions typical in meat cutting and manufacturing plants, and is inherently too slow to keep pace with the necessary throughput demanded by the large scale manufacture of meat products.
There is rather less flexibility where pig loins show colour variability, since the eye muscle is less suited to tumbling or massaging. Where flaws in such colouration occur in this cut it usually results in down-grading, or possibly routing to a different product line, for example where the cut receives some heat treatment which can reduce some types of variability in colour.
A common type of flaw in colour in loins is dark areas against a paler background, although instances occur of loins exhibiting both pale and dark areas against a more normal meat colour. Other colour variability flaws include "blood splash" and bruising, although neither type of flaw is unique to loins.
One aspect of variability in colour of loin muscle which may be considered desirable by some markets is the presence or absence of visible fat within the loin muscle. This characteristic, termed "marbling", is believed to be linked to good eating quality in pork and beef. Excessive marbling, however, may be downgraded on its appearance; thus, intramuscular fatness is another example where the distribution of fat, rather than just its absolute amount, is linked to quality and grading.
When the quality of a particular cut of meat influences the type of product made from that cut, as is the case with most of the forgoing examples, it usually also affects the financial value of the cut. Such alteration in the value of a cut must also change the net return on the carcass from which the cut originated. Existing carcass grading systems cannot easily accomodate value fluctuations of this type which only arise after grading, once breakdown of the carcass not primals has begun; since grading should ideally reflect the overall value of the carcass, this fact highlights an inherent weakness of these systems.